1. Field of the Invention
The invention relates to an inclination measuring method and device for measurement of angles relative to a horizontal plane. The invention in particular relates to a sensing method and device using electrical capacitance to measure angles.
2. Description of the Prior Art
A number of known inclination measurement devices utilize a fluid or fluids in a chamber with two or more electrodes that are partially covered by the fluid(s), with the covered electrode areas being dependent upon the angle of inclination. Such devices are typically a conductive type or capacitive type. In a conductive type device, the fluid has a specific conductivity, and as the contact area between the fluid and a pair of electrodes varies, the resistance between the two electrodes varies. The fluid in this case must electrically contact both electrodes for proper operation and the conductivity of the fluid must be carefully controlled for repeatable performance. In a capacitive type of device 1 (see FIG. 1), a highly dielectric (i.e., non-conductive) type fluid 2 is used. As the fluid-covered (i.e., wetted) area of two electrodes 4,6 is varied, the electrical capacitance C across the two electrodes 4,6 varies, with the change in capacitance varying with the angle .phi. of inclination. To obtain reasonable values of capacitance, either the electrode 4,6 surface areas must be large or the spacing g between the electrodes 4,6 must be small. This requires either a large assembly or, for minimal electrode spacing g, difficult-to-obtain close manufacturing tolerances and problematic fluid meniscus effects. Thus the prior art capacitive sensors have significant drawbacks in terms of manufacturing, size and/or accuracy.
These drawbacks also exist in other prior art devices using a matched pair of sensor electrodes in a dielectric fluid with each electrode being in opposition to a common electrode. In these devices the capacitance between the first sensor electrode and the common electrode is compared to the capacitance between the second sensor electrode and the common electrode, and the difference in the two capacitances indicates the inclination of the device.